No its just every 30 days. They can only enter your name in the DOJ website for a HG every 30 days. The background check is done before you pay typically. then its just 864,000 second wating period.
No the guns are not cheaper from state to state. The price difference is in what you pay in taxes. Take TX for instance or NV there is no state tax so, her if you buy a $1K gun you will pay $90 in tax and there its just $1K. The DROS is pretty much the same nation wide also. Its jus there you pay per visit and here you pay per serial number. They do not register your guns in other states or at least most other states.
Just curious why you want to be an armed security guard? You have taken most of the classes whay don't you take the additional 2 and become a range officer or private security where there is some money to be made. Better yet if the law enforcment is your thing give the coast guard a try, fish and game is always looking for people and so is the forest service. If you do the CG, they are law enforcement and you would be a sheo in for the Police force or one of the other Fedral LE agencies.